Inert gas-shielded arc welding electrode



United States Patent Ofiice 2,695,946 Patented Nov. 30, 1954 INERTGAS-SHIELDED ARC WELDING ELECTRODE Louis A. Conant, Tonawanda, N. Y.,assignor to Union Carbide and Carbon Corporation, a corporation of NewYork No Drawing. Application November 4, 1952, Serial No. 318,750

3 Claims. (Cl. 2198) This invention relates to inert gas-shielded arcwelding of the kind disclosed by Meredith Patent No. 2,342,086, and moreparticularly to an improved non-consumable, refractory metal electrodefor use in such welding in a stream of gas composed of argon, or helium,or any suitable mixture of argon and helium.

Heretofore, commercially pure tungsten, or thoriated tungsten, in theform of a diameter rods have been used as electrodes in this type ofwelding; thoriated tungsten being preferred over tungsten, because ofits better characteristics with respect to contamination losses, opencircuit starting voltage, are starting losses, and are stabilization.However, it has recently been suspected that in such use thoriatedtungsten electrodes may be toxic due to the volatized thoria, and also,unless some additional protection is provided, may be dangerous to thehealth of people in the vicinity due to ingested thorium with subsequentharmful internal radiation of alpha, beta and gamma rays therefrom.Thoriated trungsten electrodes also are somewhat more expensive thantungsten electrodes.

There exists a need, therefore, for a refractory metal electrode for usein inert gas-shielded arc welding, which is safer, non-toxic, cheaper,and also better even than thoriated tungsten with respect tocontamination losses, open circuit starting voltage and operatingvoltage.

The main object of this invention is to provide a novel electrode whichsatisfies such need, and which is safe and inexpensive to manufactureand easier to fabricate. Another object is to provide an electrode forsuch use that is lighter in weight than either tungsten or thoriatedtungsten electrodes.

According to the invention such objects are accomplished by providing-anon-consumable inert gas-shielded arc welding electrode which iscomposed of tungsten having dispersed therein a minor amount (0.5-10%)of calcium oxide, 2% of the latter being satisfactory.

Mixtures of tungsten and the appropriate chemical component, such ascalcium acetate powder, to yield the metal oxide are used to prepareingots approximately x A x 18 inches by conventional powdermetallurgical techniques (pressing). These ingots are sintered at 2000C. or above by passing an electric current through them. The ingots arethen drawn or swaged to the final dimensions. Considerably more detailcan be obtained from standard text books on the subject, such asTungsten by Smithells, or Tungsten by Li and Wang.

Starting voltage The starting voltage characterizing an electrode undergiven starting conditions is an important quantity as it determines theopen circuit voltage requirement on the welding source. Electrodes whichexhibit a relatively low open circuit voltage requirement for startingwill permit a stable arc to be established almost instantaneously, thusminimizing labor and material expenses particularly in machine welding.Comparison was made with commercially pure tungsten and thoriatedtungsten electrodes. At the time of these tests only inch diametercommercial thoriated tungsten electrodes were on hand. These weremounted in a torch of the type disclosed by Breymeir Patent No.2,468,804. A inch diameter commercial tungsten rod was similarly tested.

Exploratory tests disclosed conditions which not only indicated startingvoltage differences, but also permitted results to be obtained withsatisfactory reproducibility.

The test conditions were (1) a hemispherical electrode tip, (2) a coldarc length of 0.050 inch, (3) an established are of 80 amperes, DCSP,(4) an argon flow rate of 15 cfh, and a fairly massive stainless steelanode or workpiece. A motor-generator was used as the power source;external field excitation was used to extend the open circuit voltagerange below 40 volts. Gap breakdown was initiated by the output from ahigh-frequency stabilizer. The starting voltage under these conditionswas taken to be the minimum open-circuit voltage for which reliable andinstantaneous starting resulted in at least nine of ten consecutivetrials. Since no attempt was made to control precisely such factors assurface conditions except for initial grinding, and particularly sincethe instantaneity was a matter of the observers judgment, precisereproducibility of the data was not always observed. Thus, an estimatedlimit of error of about $5 volts is to be associated with these data.This limit is set largely by experienced intuition with weight placed onthe observed ranges of open-circuit voltage for transition from percentstarting to a condition of no starting.

Electrode starting losses Electrode weight loss during starting withhigh-frequency voltage is significant in connection with spot weld ingand with repetitive machine welding of small parts or short lengths ofscam. Starting loss characteristics were established by determining theweight change produced by successive are strikings. Equipment wasconstructed in which motor-driven cams actuated switches permittingautomatic execution of a 16.5 second operation cycle as follows: (1)line power was supplied to a rectified welding current source having anopen-circuit voltage of about 70 volts, (2) line power was supplied to ahighfrequency stabilizer for about 0.5 second, the output breaking downthe arc gap and establishing a ampere DCSP argon-shielded arc, and (3)following operation of the are for approximately 1.5 seconds, power tothe Welding current source was interrupted. A short arcing" time wasselected to reduce contributions to weight changes from arcing alone anda cycle period large with respect to the time of arcing was used toprovide a reasonable interval for cooling the Work metal to avoid puddlebuildup problems. Following original adjustment of the arc length to0.050 inch, no further manual adjustment in arc length was madethroughout the test. A stainless steel anode (workpiece) was utilizedwith an arc current of 110 amperes DCSP. The argon flow rate was 20 cfh.

Wt. Change after 100 Starts Electrode Trial I Trial II Avg.

M M V W (Commercial) 6.7 4.1 5.4 2% CaO-W O. 6 0. 6 O. 6

Differences due to torch design and/or electrode geometry appear in thedata for commercial tungsten electrodes. However, it is apparent thatthe new electrodes are substantially better than commercial tungstenelectrodes with respect to starting losses.

Operating voltage On the other hand in welding thin materialsburn-through and other undesirable heating effects are to be avoided.One method of doing this is to decrease the are power by decreasing thearc voltage. The table below shows that electrodes of'the inventionproduce appreciable lowering of the'arc voltage;

Another method of reducing are power is by reducing the arc current. Theextent to which this can be done is determined by the lower currentlimit for stable operation. This in turn is a function of electrodecomposition. It has been shown that stable operation can be realized atlower current than that found for standard tungsten electrodes by usingthori'ated tungsten electrodes. Such a determination has not been madefor the electrodes of the invention. However, since it is believed thatthe starting voltage requirement is an indication of the lower currentlimit for stable operation, inasmuch as electrodes having low startingvoltage requirements can be expected to operate stably at relatively lowarc currents.

The following measurements were taken with a 150 am pere DCSPargon-shielded arc on stainless steel. The argon flow rate was 20 cfh.At least five readings were obtained at each length setting, theaverages being shown in the data table. These data include the IR dropalong the electrode.

Arc Voltage at- Electrode Length Length W (Commercial) 8.5 10. 1%'lhOz-W (Commercial) 8. 2 10.5 W (Commercial) 8. 4 10.7 2% CaO-W 8.310.5

Electrode performance on stainless steel Weld beads were made to comparethe influence of electrode composition on penetration andthe amount ofwork metal melted. These welds were made at a welding speed of about 40ipm on 0.055 inch thick stainless steel with 150 ampere DCSP arcs. Thecold arc length was 0.050 inch and the argon flow rate cfh. The datapresented below wereobtained from single cross sections. The dependenceof melted area on are voltage is shown by these data.

ELECTRODE INFLUENCE ON BEAD SHAPE data which at first glance appears tobe a large one. It

is felt that this effect is primarily due to the ditference in thermalexpansion of the electrode as a result of differences in the electrodegeometry and torch cooling etficiency. Comparing the lengths of 7 inchdiameter sections in the two cases one expects for the experimentalelectrode roughly six times the expansion of the standard. Moreover,experience has shown that it is not too far afield to assume theoperating length to be about 50% of the cold setting when standard LindeHeliarc equipment is used. Such considerations yield arc voltage resultsshown in column four as calculated from the data of the previoussection. In most cases the agreement is satisfactory.

The last column has been calculated to give a rough metal meltingefficiency comparison.

Contamination losses Losses of electrode by low melting alloy formationfollowing accidental contact with molten metal are likely to be one ofthe most important factors in determining.-

electrode life, particularly in hand welding applications. For thisreason, measurements were made to determine the ability of variouselectrodes to withstand contamination by.

molten stainless steel. A 200 ampere arc was maintained on a stainlesssteel anode for two minutes; the electrode was then forced into themolten pool of the anode four times in succession (the arcre-establishing itself between:

immersions) and finally operated for another two-minute penod'to allowimpurities on the electrode to burn-01f. During the entire proccsstheargon flow rate was'25 cfh;

Electrode tggg g g W (Commercial) 300-460 2% ThOz-W (Lintle)... 106 1%ThOz-W (Mallory). 92 2% CaO-W sten and calcium oxide in the ratio ofabout 2% by weight of calcium oxide, the balance being commercially puretungsten.

3. An electrode for gas-shielded metal fusing arc processes, composed ofrefractory metal comprising tungsten containing a relatively smallamount, i. e. 0.52.0%, inclusive, of calcium oxide.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,792,943 Terry Feb. 17, 1931 2,515,559 Lancaster et al. July18, 1950

1. A NON-CONSUMABLE INERT GAS-SHIELDED ARC WELDING AND CUTTING ELECTRODECOMPOSED OF TUNSTEN HAVING DISPERSED THEREIN A MINOR AMOUNT (0.5%-10%)OD CALSIUM OXIDE.